Github Avoid truncating PR titles

extension.js

// ==UserScript==
// @name         Revert GitHub PR Title Truncation
// @namespace    https://github.com/lionel-rowe/
// @version      0.4
// @description  Revert GitHub PR Title Truncation
// @author       https://github.com/lionel-rowe/
// @match        https://github.com/*
// @icon         https://www.google.com/s2/favicons?sz=64&domain=github.com
// @grant        none
// @run-at       document-start
// ==/UserScript==

// https://github.com/orgs/community/discussions/12450

// @ts-check
/// <reference lib="dom" />
/// <reference lib="dom.iterable" />

/** @typedef {{ title: string, body: string }} Content */

const ELLIPSIS = '…'

new MutationObserver(untruncate).observe(
    document.documentElement,
    { childList: true, subtree: true },
)
untruncate()

function untruncate() {
    if (!location.pathname.includes('/compare/')) return

    const $title = document.querySelector('[name="pull_request[title]"]')
    const $body = document.querySelector('[name="pull_request[body]"]')

    if (!$title?.checkVisibility() || !$body?.checkVisibility()) return
    if (!($title instanceof HTMLInputElement) || !($body instanceof HTMLTextAreaElement)) {
        throw new TypeError('Unexpected element types')
    }

    reflow($title, $body)
}

/**
 * @param {HTMLInputElement} $title
 * @param {HTMLTextAreaElement} $body
 */
function reflow($title, $body) {
    const result = getReflowed({ title: $title.value, body: $body.value })
    if (result == null) return
    $title.value = result.title
    $body.value = result.body
}

/**
 * @param {Content} content
 * @returns {Content | null}
 */
function getReflowed({ title, body }) {
    if (title.endsWith(ELLIPSIS) && body.startsWith(ELLIPSIS)) {
        const m = /\n\s*/.exec(body)
        const first = body.slice(0, m?.index ?? undefined)
        const rest = m == null ? '' : body.slice(m.index + m[0].length)

        return {
            title: title.slice(0, -ELLIPSIS.length) + first.slice(ELLIPSIS.length),
            body: rest,
        }
    }

    return null
}